Wide band transmit receive switch



P 1953 L. D. SMULLIN 2,653,300

" WIDE BAND TRANSMIT RECEIVE SWITCH Filed Oct. 10, 1945 FIGJ A l j 5 gjjlitj IN V EN TOR.

LOUIS D-SMULLI N BY 70w HHMQ. 1AM

ATTORNEY Patented Sept. 22, 1953 WIDE BAND TRANSMIT RECEIVE SWITCH Louis D. Smullin, Arlington, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Applicationoctober 10, 1945, Serial No. 621,567

2 Claims. (01. 333-13) My invention relates in general to switching devices and more particularly to such devices as are used with radiant energy transmitting and receiving systems.

In many applications of radio transmitting and receiving apparatus such as radio-echo object locating systems it is desirable to employ extremely high power transmitters and sensitive receivers. Furthermore, it is expedient to employ a single antenna which is used both for the radiation of transmitted energy and the reception of that portion of the transmitted energy which is reflected from distant objects. Such a system eliminates the possibility of parallax between separate transmitting and receiving antennas and greatly simplifies the adjustments necessary in orienting the antenna system as well as reducing the bulk and complexity of the radiating apparatus required.

Clearly, with a single antenna it is possible to use one transmission line leading thereto into which both the transmitter and receiver must be connected. Normally in a radio object locating system the transmitter generates a pulse of oscillatory energy which is passed through the transmission line to the antenna system and radiated into space. The oscillator is then maintained inoperative for a predetermined periodof time so that echoes from reflecting objects may be received at the antenna and be passed down the transmission line to the receiver.

There are two problems which arise in connection with this type of system. The first is that the oscillator power is sufficient to overload the receiver and possibly to burn out the sensitive detecting device used therein. Since both oscillator and receiver are connected into a transmission line, means must be provided to disconnect the receiver from the transmission line during generation of oscillatory energy. Secondly, faint echoes may be dissipated in the oscillator instead of being conducted only to the receiver. Therefore it is necessary to provide automatic apparatus which performs in effect the function of a switch which will alternately connect the transmitter and the receiver to the antenna. Devices of this nature are known in the art as duplexers, polyplexers, and "transmit-receive, or T-R switches. In a more specialized sense T-R switches are those devices used to disconnect the receiver during transmission of energy and R-T or anti-T-R switches are those used to disconnect the oscillator during signal reception. A general discussion of the switches may be found in the application of Harold K.

Farr, Serial No. 488,098, filed May 22, 1943, and entitled Apparatus for Duplex Radio Transmislsion and hence will not be given in detail here. My invention may be employed either as a T-R or as an anti-T-R. switch although only the anti- 1 T-R embodiment is described herein. Accordingly, it is one object of my invention 1 to provide a T-R switch for a radio system. Another object of my invention is to provide an anti-T-R device which is responsive to a band of frequencies. Still another object is to provide a tunable 1 anti-T-R box. Yet another object is to provide an anti-T-R. 1 box with a readily replaceable electron discharge element.

Briefly, my invention contemplates the construction of a tunable T-R or anti-T-R box by coupling to a cavity containing a spark discharge t element, a variable susceptance in the form of g a second cavity which is tuned by a single movlable probe inserted therein. The device is adapted to be employed with a transmission line {of the wave guide type, although with modifications it may be used with a coaxial line.

The construction and operation of my invention will be more apparent upon reference to the following specification, claims, and to the drawings in which:

Fig. 1 represents a cross-sectional view of an anti-T-R device constructed according to one embodiment of the principles of my invention; and

Fig. 2 is another view of the device shown in Fig. 1.

Referring now to Fig. 1, a cavity 5 is bounded by a conducting box or shell 6 forming a cavity resonator. Threaded pin 1 is fastened at one end to shell 6 and a nut 8 is screwed thereon. A probe III of some suitable conducting material passes through shell 6 and projects into cavity 5, being held and guided by probe support I l which is fastened to shell 6. One end of probe [0 is attached to probe holder 12 which in turn engages with nut 8 in the fashion shown in the drawing. Probe holder I2 is held in firm contact with nut 8 by spring l3.

A circular opening is bored through each-side of shell 6 and the shell is split into two portions along a line passing through the center of these circular openings and parallel to the narrow end of the shell. The openings thus formed are adapted to receive an electron discharge tube of the spark gap variety which may consist, as shown in Fig. 1, of two circular plates I 5 and I 6,

usually of copper, the center portions of which are formed into roughly conical points with a small gap between them. Plates .5 and is are enclosed by a glass shell ll with the exception of a circular lip which fits snugly against a shoulder formed in bushings i3 and 28. A retaining means (not shown) will normally be employed to maintain bushings l9 and 28 in firm contact with the projecting lips of the spark gap electrodes.

It will be noted that one end of the cavity is open so that oscillatory energy may be admitted thereto. In practice this end is attached to a wave guide energy transmission means. It may be found desirable to seal off thisend with a window of glass or some such material which will not substantially disturb the passage of energy through the opening.

In Fig. 2 there is shown a top view of the shell or box which is shown in cross section in Fig. 1. The circular opening for the discharge tube as well as the line on which the box is split can be seen. Projections 22 "and 23 are drilled and tapped to take "screws 2'4 and 25 which hold the two portions 'of the box together. 3

Although cavity '5 is physically continuous, its? action is effectively that of two cavities joined in some such plane as that indicated by A-A in Flgl 1. The volume containing the spark gap dis-i charge tube is essentially a normal non-tunablei anti-T 12. box while the remaining volume is a separate cavity, the susceptance of which is in parallel with the anti-T-R cavity. 1

It can be seen that if the anti-T-R cavity were tuned conventionally by multiple probes ori screws which act as inductors projecting radi-i ally into it, the maxi-mum inward extension of thei tuning members, and hence the highest resonant} frequency'of the cavity, would be governed by the? glass envelope l! of the spark gap tube, and the; lowest frequency to which the cavity would tunef would be limited by the diameter of the cavity, withthe'screws withdrawn. 'In apparatus for use at very short wavelengths the diameter of glass; envelope [-7 approaches the diameter of the cavity and hence the tuning range is necessarily limited, in some cases being as low as two or three per cent. 7 r

This =difiiculty is obviated in my invention in which the auxiliary cavity is capacitively tuned by probe It. Bylocating the probe at the electrical center of the tuning cavity in order that the capacitive effect between the end of the probe and the opposite wall of the cavity (the capacitor s'hownin dashed linesin Fig. l) is a maximum, it is possible to produce, with a single tuning control, a greater frequency range than can be brought about by a plurality of inductive tuning elements inserted into the anti-FT-R cavity itself. The "susc'eptance variation of a tunable resonant cavity as employed in my invention is essentially from to In one embodiment of my invention, variation of the susceptance over this range will alter the resonant frequency of the T--R cavity by approximately 12 per cent.

Acavity is not the only auxiliary tuning means which may be employed, it being also possible to use the susceptance of a shorted section oftransmission line coupled to the main cavity by means of 'either'a 100p'0r an iris.

In practice the device'as described aboveis attached to the wall of a wave guide having an aperture therein which-substantially corresponds in size and shape to the opening in box '5. This opening will normally be situated at a distance "from the branch line leading to thereceiver substantially equivalent to a quarter wavelength of the oscillatory energy in the wave.

In its essential principles of operation, my invention is similar to other anti-T-R devices of its type. However, it has an outstanding advantage in the fact that its resonant frequency may be varied. In many cases, the device will be used with a suitable oscillator, thus it is necessary to have an adjustable anti-'T-R box to allow for efficient operation of the entire system at any frequency within the range over which the oscillator is tunable. Inaddition, the versatility of a tunable anti-T-R box is such as to permit use of it with entirely different types of systems, providing the frequencies of the various oscillators with which it may be employed are not too widely separated.

It will be understood that what has been shown and described hereinabove is a preferred embodiment of the present invention, however modifications and adaptations may be made therein without departure from the inventive principles thereof. Hence, I claim all such modifications and adaptations as may fall fairly within the spirit and the scope of the hereinafter appended claims.

What I claim is:

1. A tunable switching device for use with electromagnetic energy of a wide band of frequencies comprising a conductive chamber, said chamber being eifectively composed of first and second contiguous cavity resonator sections, one end of said first section being adapted for coupling to electromagnetic transmission means, a spark discharge device mounted solely in said first section, said second section having a high Q at all times, and means within said sec- 0116. section for tuning said second section.

2. A tunable switch for use with electromagnetic energy of a wide band of frequencies comprising a conductive chamber having a rectangular cross section and two broad and two narrow sides, said chamber being effectively composed of first and second contiguous cavity resonator sections, one end of said first section being provided with an aperture for coupling to electromagnetic energy transmission means, a gaseous spark discharge device mounted solely in said first section, and oriented to have the path of the spark discharge parallel to the narrow sides of said chamber, said second section having a high Q at all times, a conductive probe mounted in said second section and positioned at the "electrical center of said second section, parallel to the discharge path of said discharge device, and means for varying the depth of penetration of said tuning probe into said second section.

LOUIS D. SM-ULLIN.

References Cited "in the file of this patent UNITED STAT-Es PATENTS 

